This invention relates to a pulmonary ventilator controller system for use by an anesthesiologist to ventilate the lungs of a paralyzed and anesthetized patient undergoing surgery, and more particularly relates to such a controller that is capable of automatically altering the target values dialed in by the anesthesiologist for breathing rate and inspiration time to make them compatible with the maximum flow rate and maximum capacity of the ventilator being controlled.
In a pulmonary ventilator system of the prior art, the anesthesiologist-operator is required to orchestrate the control of the separate ventilator operating parameters, e.g. driving gas flow rate, breathing rate, expiration times and inspiration time to achieve a desired delivery rate of breathing gas. Breathing gas delivery rate is called minute volume and is usually measured in liters per minute. When using a prior art ventilator such as that described in my patent application Ser. No. 685,906, filed Dec. 24, 1984, wherein the minute volume of the breathing gas is also equal to the total amount of driving gas provided each minute, an oscillator periodically turns on and off a solenoidally actuated valve in the input line supplying the driving gas to the ventilator. The anesthesiologist separately adjusts a driving gas flow rate determining valve, the breathing rate by adjusting the frequency of the oscillator and the ratio of expiration time to inspiration time by adjusting the duty factor of the oscillator. It is easily possible to make the mistake of making a combination of these adjustments that would call for a greater flow rate than the driving gas source can actually provide, or call for a tidal volume larger than the capacity of the ventilator.
It is therefore an object of the present invention to provide a pulmonary ventilator controller that is simpler to operate and is safer and more reliable in use.